My dad remarried six months after my mom died. It did not upset me in the least. Dad was miserable after mom's death. He needed someone and so did she (she was divorced). They were very happy the few short years they had together until Dad died. I hate to think how sad and lonely his last few years would have been if he hadn't remarried.
Getting remarried does not mean you loved your first spouse any less. It just means that life goes on.
6 Months?? When did they start to date? I hope it wasn't while your mom was still alive!
And, no, I have not lost a spouse. I have never been married. I was in a long term relationship that ended (yes, I know it's not the same as marriage, divorce and widowhood, but bear with me) and there's no way I would have been able to enter another relationship so soon, let alone get married. Besides, "rebound" relationships don't last 99% of the time.